Method of strip annealing aluminum foil



Feb. 13, 1940. M. SCHON METHOD OF STRIP ANNEALING ALUMINUM Foil:

Filed Aug. 12. 1956 fiaahew SckonA Sham Patented Feb. 13, 1940 PATENT OFFICE METHOD or s'rmr ALUMINUM Matthew Schon,

Crown Cork & Seal Company, Inc., Md., a corporation of New York ANNEALING W O L Baltimore, Md., assignor to Baltimore,

Application August 12, 1936, Serial No. 95,647

1 Claim.

This inventiomrelates to a continuous method of strip annealing aluminum foil. Aluminum foil is commercially available in the form of rolls of continuous strips or sheets having a very thin gauge of about .002" and consisting of substantially pure aluminum. Such foil is used, among other things, as a' spotting or lining material for container closures as well as for a variety of wrapping purposes.

By a continuous method of strip annealing" is meant the continuous feeding of the aluminum foil, as for example, from a roll, to and through an annealing instrumentality and the rewinding of the annealed foil. This method is distinguished from, and marks a decided advance over, the generally accepted and, in fact, heretofore considered best, practice of batch annealing.

Batch annealing is slow in that a coil of aluminum is heated in an oven for a period of 12 to 14 hours at about 600 F. or between 650 F. and 850 F. and then cooled for a similar period. Consequently, it is necessary to constantly keep a large supply on hand which is not economical, since in most cases the minimum quantity which must be kept available amounts to about a fortyeight hour supply. Furthermore, since the annealing operation is conducted with the aluminum foil in the form of a coil or roll, it is recognized that it is not possible to secure a uniform 3o anneal nor impart constant characteristics throughout the strip or sheet of foil. Moreover,

- the batch annealing method has the equally important disadvantage that the oil film with which the toll is usuallyco'ated is not removed by the annealing operation. The commercial foil annealed by the batch method therefore still has an objectionable oil film which is difficult and expensive to remove and highly undesirable, as will be appreciated, where the toll is used as a spotting or liner material for container closures and is in contact with a food or chemical product.

and likewise to be avoided where the foil is employed as a wrapper. I

It is the object of the present invention to produce a foil annealed so as to have uniform characteristics and properties, free of objectionable oil film, and to achieve such results by a method which is both rapid and efllcient.

' While continuous methods of strip annealing have been employed, for example, as described in the United States Patent to Webster 1,911,666, so far as known, no satisfactory commercial method for strip annealing aluminum foil has been developed. This is probably due to the dimculties attendant upon the treatment of the relatively thin, weak foil on the one hand, and the necessity for a simple and adequate control on the other. a

I have discovered that aluminum foil may be continuously and uniformly annealed with com- (Cl.148-13.1) a

plete volatilization of the oil film and without producing wrinkling or matting or tearing of the foil by (1) travelling the foil at a constant speed and under a constant tension, (2) controlling the heating temperature and the time period of heating, and (3) cooling the strip substantially immediately after the heat treatment by a positively controlledv reduced temperature and for a relatively shorter time period than the heat treatment, followed by air cooling at normal temperature.

In practicing the method of the invention, and by way of example, a coil of aluminum foil having a thickness-of about .002" more or less, and having the usual oil film upon its surface, is drawn continuously from a roll by means which also act .as a tension device, and the strip is passed over and in contact with a heating surface. The temperature, the area of the heated contact surface, and the time period which is a resultant of the size of the contact area and the speed of the strip are controlled so that the strip is uniformly heated throughout. I have discovered that high temperatures above the melting point of aluminum, e. g., up to 1275" F. may be used because the foil has an oxide coating on both from the heating to the cooling instrumentality and given a quick cooling by contact with a cooling surface having the required temperature. This quick cooling, however, is for a relatively shorter time period than the heating and is followed by'cooling the foil at normal atmospheric temperature in the air and while it is being carried away from the cooling instrumentality and rewound as a coil or roll. The proximity of the heating and cooling contact surfaces, the speed of the. foil, and the cooling area presented to the strip material govern the quick cooling of the foil. The aircooling is controlled by the speed of the strip and the proximity of the rewinding means to thecooling instrumentality, but cooling of the annealed foil as a roll under atmospheric conditions, will take place until the foil reaches normal atmospheric temperature.

Preferably the heated surface contacts with feet per minute;

or a reducing atmosphere such as hydrogen, istated at a proper speed by the motor or a separate provided within the hood, in some cases.

The tension exerted on the strip at all times is constant, but is strong enough to avoid wrinkling and so'controlled as to prevent forming a matted surface or tearing the foil. The speed of the foil as it travels from the roll continuously past the contact surfaces and is rewound, into a coil of-annealed aluminum foil, is maintained constant. Both the tension on and the speed of the foil are controllable, as are the temperatures to which it is subjected, and the contact areas over which the strip passes, so that a varied set of conditions may be employed which will develop the desired physical properties and assure that the foil will be uniformly annealed.

The temperature of the heated contact surface may be varied from about 700 F. to above the melting point of aluminum; the speed of travel 01'. the coil over the heating and cooling surfaces may be controlled at from 13 feet a minute to 22.5 the heated foil may be quick cooled to temperatures of from 340 F. to 600 F., depending on the heat treatment; and the ratio of the area of the heating contact surface to the area of the cooling contact surface, presented to the foil, may vary from 2 to 1 to 4 to 1.

In the appended drawing, I have illustrated one method of carrying out the invention as well as the apparatus preferred for the purpose, but it is to be understood that the method may be carried out in other ways and upon modifica-' tions of the machine illustrated.

Referring to the drawing, the numeral I 0 shows a. roll or coil of foil freely mounted on a shaft II. The foil is continuously removed from the roll by engagement between a pair of rubber coated pinch rolls I2, operable at a variable speed from a suitable motor or other prime mover. The pinch rolls propel the foil through an opening I3 in the wall of the hood I4 which is suitably bushed or rendered air-tight and beneath an adjustably mounted guide roll I5. to and over the surface of a heating roll I6. This heating roll is rotated by the same motor as the pinch rolls or by a separate prime mover, but at a rate relative to the speed of rotation ofthe pinch rolls as to obtain a proper heating and to assure the required constant tension being exerted on the foil, 1. e., to avoid wrinkling or matting of the foil.

The surface of the roll IS, with which one side of the travelling foil is in contact. is heated by an internal means such as electrical resistance coils I1, which are suitably regulable to control the temperature of the heated surface.

The surface area of the foil is also controlled.

the rotating roll I6 acts to support and to propel the foil along its continuous path at a constant speed in conjunction with the pinch rolls I2.

During this direct heat treatment, the oil film, usually to be found on the foil, is continuously volatilized and the final product is free from this objection. Beneath the roll I6 is an oil doct r I8 for removing any oil residue which may collect thereon.

The foil immediately following the heat treatment is continuously passed in direct contact with and beneath a cooling roll I9 which is roby means of guide rolls,

prime mover to preserve the correct constant In the present instance, the diameter of the roll I9 is that of the heating roll I6. The area of contact of the roll I 9 with the strip is relatively much smaller than that provided in the heat treatment, so that the cooling period is reduced. This contact area, however, is regulable as described above, or by adjusting the position each other.

The diameters of the rolls I6 and I9 may vary as well as their respective areas presented to the strip to develop any desired properties in the foil, but in all cases a relatively brief positive cooling is considered necessary. I

The annealing, as will be appreciated, takes place during travel of the strip over and by contact with the several rolls and within the hood I4.

For example, a foil of .002 gauge is travelled at a speed of 22.5 feet per minute over the roll I6 having asurface temperature of about 995 F. and is delivered in satisfactory annealed condition, devoid of oil film from the roll I9 at a temperature of about 600 F.

It will be noted that the heated surface of the roll I 6 presented to the foil is substantially onehalf of the cylindrical surface-of the roll, while the cooling area presented by roll I 9 is somewhat less than one-half the cylindrical surface.

Also, the foil is heated on one side and its opposite surface presented to the cooling roll.

From the cooling roll I9, the foil is continuously travelled through an opening I3 in the opposite 22 and particularly to control foil, so as to maintain it constant in combination with the rotating rolls I6 and I9 and the tension device I3, and also to maintain the strip at a constant speed.

as a continuous operation.

I claim:

The method of continuously annealing a conof the rolls I6 and I9 to 

